Content area
Full Text
History and Evolution
The first edition of the Highway Capacity Manual (HCM) was published in 1950, and its aim was to provide "a practical guide by which the engineer, having determined the essential facts, can design a new highway or revamp an old one with assurance that the resulting actual capacity will be as calculated.''1 The HCM 1965 first introduced the concept of levels of service (LOS), which have been defined based on a selected performance measure such as speed, or density.-' As highways became more and more congested, our understanding of traffic operations evolved, and so did the needs of the practicing transportation professional. It became significantly more important to evaluate congested operations, to consider multiple modes and their interactions, and to obtain a variety of performance measures and tools, including simulation. As a result, the HCM has evolved so considerably that the Highway Capacity and Quality of Service Committee (HCQSC) of the Transportation Research Board (TRB)-the body that governs the publication of the HCM-decided to add the subtitle "A Guide for Multimodal Mobility Analysis" in the most recent edition (expected to be published by TRB in the third quarter of 2016) to underscore those elements. Additionally, this edition is now called the 6th Edition (rather than having a year attached to it), with a version number provided for each chapter, to allow for more frequent updates of individual chapters or smaller portions of the manual as new research becomes available.
This article provides an overview of the HCM 6th Edition and serves to familiarize transportation practitioners and researchers with the extensive set of analysis tools the publication provides.3 These analysis tools represent the most recent research on traffic operational analysis, as judged by the HCQSC, whose members include a wide cross-section of transportation professionals within the United States and abroad, representing the public sector, the private sector, and academia. The HCM was reviewed by committee and subcommittee members as well as numerous external evaluators- in total, approximately 200 reviewers who provided a total of 3,331 comments on the draft materials developed by the contractor, Kittelson and Associates, Inc. The comments were vetted by the HCQSC, which worked with the contractor over a period of three years to revise and finalize the document. Official...